Though it is widely believed that all whales cannot smell, evidence points to the contrary, including indigenous knowledge, anatomical, genetic and behavioral data. Many whales face a feeding “problem” that is similar to tubenose seabirds (e.g. petrels, shearwaters). Classic seabird studies reveal that tubenoses use olfactory-mediated foraging by orienting into the wind upon approaching experimental “plumes” of food scent. More recent work has discovered some marine birds are attracted to dimethyl sulfide (DMS), a volatile chemical byproduct of algae (phytoplankton) when it is being fed upon by zooplankton. Hence, for a marine predator like a seabird, DMS is a potentially reliable chemical indicator of a zooplankton food source and a rich place to feed.
Until recently, any behavioral evidence indicative of a whale's ability to smell was completely lacking. The inventor's recent field research on Humpback whales (Megaptera novaeangliae) in southeast Alaska revealed that whales orient into the wind significantly more often than expected by chance alone (n=231 whales, df=1, X2=54.6, P<0.0001). This pattern is consistent with a capacity detect chemical stimuli carried by wind. Other baleen whale species (Suborder Mysticeti), like humpbacks, may also detect air- or water-borne chemical stimuli, as they have measurable olfactory structures and large trigeminal nerves, which may also perceive chemical irritation. Toothed whales, however, such as dolphins or Sperm whales (Suborder Odonticeti) appear to lack olfactory anatomy, but may still sense chemical irritation.
When whales or other marine predators feed, they are likely exposed to a number of biologically-relevant chemical stimuli in both air and seawater that are associated with a productive food patch. For example, zooplankton grazing on algae rip open algal cells and release the algal metabolite DMSP (dimethyl sulfoniopropionate) into seawater. DMSP rapidly breaks down into DMS (dimethyl sulfide) and acrylic acid, or it may follow another degradation pathway to produce methanethiol. Hence, the chemicals are indirectly indicative of food, as they are not directly derived from zooplankton prey itself, but rather derived from the plant food (algae) that zooplankton are actively consuming. Different marine habitats exhibit different concentrations of the aforementioned chemicals. Concentrations are positively associated with areas of high productivity, but they can vary by season and geographic location. For example, DMS concentrations in highly productive “hot spots” of Arctic Oceans can reach 4.0-7.0 nM, whereas underneath marine ice they may be only 0.4-2.0 nM.
Synthetic and/or natural sources or mixtures of biologically-relevant attractants (e.g. DMS, DMSP, acrylic acid and/or methanethiol) could provide a very new and powerful method to attract baleen whales. The luring mechanism mimics a high-quality feeding site, and thereby attracts baleen whales in a predictable direction, up a chemical gradient, toward an artificial stimulus source. An alternate embodiment of this idea includes not only whales, but a variety of other marine vertebrate predators (e.g. sea turtles, basking sharks, seals, sea lions, birds, fish), which have been positively correlated with DMS in their environment, or shown to perceive DMS in a laboratory setting.
The aforementioned attractant or luring mechanism would fundamentally alter how humans manage the difficult task of motivating large marine creatures like whales to move in a desired direction, for instance away from a dangerous oil spill or other marine hazard. State of the art knowledge focuses on loud, acoustic deterrents, including cannon guns, pounding on hollow steel pipes (called Oikami pipes), low flying aircraft, harassment by vessels, or underwater “pingers” attached to hazardous equipment. Collectively, the state of the art “hazing” methods have a number of disadvantages. First, loud noises that aim to scare animals produce highly variable reactions, making behavioral responses erratic, unpredictable, and can include the undesirable result of an animal moving closer to a hazard. Second, even acoustic devices, such as pingers, that whales can hear but are not loud enough to cause cause hearing damage (e.g. 135 dB), have a limited underwater range (<100 m). Thus, desirable improvements of a biologically-relevant lure, include predictable, directed movement or attraction toward an attractant source, as well as a long distance range for stimulus perception. Chemical stimuli can provide both such improvements.
Management agencies in charge of marine hazards, such as oil spills, emphasize the need to have multiple tools for wildlife relocation ready to deploy during a marine emergency. Attractants are needed, but there are few, if any, relative to the variety of hazing techniques currently available. Unlike hazing, attractants are amendable to gradually and/or reliably enticing animals to move in a preferred direction.
A powerful means of attracting animals engages multiple animal senses at once. A biologically-relevant attractant has the potential to stimulate the three vertebrate chemical senses: smell, taste, and the trigeminal system. Trigeminal responses in humans, for example, include the mild irritation or tickle of mucous membranes when exposed to chemicals, such as those in ground pepper. In some whales such as the baleen whale, the trigeminal nerve is the largest cranial nerve. The compound DMS exhibits properties that produce both marked olfactory and trigeminal responses. An alternate embodiment of the lure could enhance multimodality and the attractive value of the stimulus by combining a chemical attractant with one or more cues that are perceived by entirely different sensory modalities. For example, along with chemical stimuli, one might provide an auditory stimulus, such as underwater playback of whale song.